Flow cells FC2, FC3 and FC4 can be fouled by buffer salts, standard or sample substances especially in the tubing that brings measured liquid to the sensor. The salts embed namely in the edges of drilled openings. It causes decrease of the flow area, thereby flow rate. These negative influences decrease the signal and measurement reliability. Most frequently it happens when high salt concentration solutions or solutions with impurities are used. The flows cell can be washed by pressured water using syringe.